But no, I don't want to spend the money for a pair of OPT's. Tell you what...

I have a pair of old UTC CG51AX interstage transformers. The primary is 22H measured on my LC meter, DCR is 1050 ohms. I can commit these to the cause. I would use only their primaries as the plate loads.

I figure 22H and DCR = 1050R loading a triode with an rp of 2k ohms will give a -3dB point of about 7 Hz.

Can these IT transformers deliver their inductance under a 22mA load? Well I don't know. Is there a way to infer from the L and DCR what the current capacity is?

Since the primary was intended to be a plate load (the secondary is a push-pull winding), wouldn't that primary work as a plate choke? I have no idea if there is an air gap in the core. There just isn't much info available for UTC CG51AX.

Back in 2005 on another forum, someone wrote:

"I have a pair of UTC CG51AX ITs (sorry, no link) which according to UTC can adapt just about anything to a 2A3, 6L6, or similar. The catalog doesn't provide impedence specs but claime to "match single tubes like 6C5, 6C4, 12AU7, 2A3, 5814A" to tubes like "2A3 or 6L6". There are two primary connections and 5 (I believe) secondary connections, one is ct. Ratio is specified as 2.8:1 or 3.1:1 primary to 1/2 secondary. Also the IT is rated at 5W."

I don't know how 5W translates to max current capacity before core saturation. Just Ea times Ia?

What is the lowest plate current you'd use with a 6V6-triode in this circuit?

"The CG-51AX is a Single Plate to Push-Pull Grids Interstage Driver transformer. The Primary was designed for a single 6C5, 12AU7, 6A6, 6N7, 45, 2A3 or other tubes with a maximum of 5 Watts (!); to couple to the Grids of 45, 46, 2A3, 6L6 or other push-pull audio output tubes. The Secondary can be configured for a Ratio of 2.8:1 or 3:1 Primary to 1/2 Secondary, making these interstage driver transformers very versatile. Maximum Level is 5 Watts on the Primary. Frequency Response is actually impressive for a Single Plate to Push-Pull Grids transformer that can handle significant unbalanced DC in the primary, listed as 40-10KHz + or - 1 1/2 db. Each of these vintage UTC transformers is physically about 3 1/4"H with base width of 2 9/16" x 2 9/16" which have mounting center holes at 2 3/32" square. "